General-purpose I/Os (GPIO) RM0090
197/1422 Doc ID 018909 Rev 4
7.3.15 Selection of RTC_AF1 and RTC_AF2 alternate functions
The STM32F4xx feature two GPIO pins RTC_AF1 and RTC_AF2 that can be used for the
detection of a tamper or time stamp event, or RTC_ALARM, or RTC_CALIB RTC outputs.
● The RTC_AF1 (PC13) can be used for the following purposes:
RTC_ALARM output: this output can be RTC Alarm A, RTC Alarm B or RTC Wakeup
depending on the OSEL[1:0] bits in the RTC_CR register
● RTC_CALIB output: this feature is enabled by setting the COE[23] in the RTC_CR
register
● RTC_TAMP1: tamper event detection
● RTC_TS: time stamp event detection
The RTC_AF2 (PI8) can be used for the following purposes:
● RTC_TAMP1: tamper event detection
● RTC_TAMP2: tamper event detection
● RTC_TS: time stamp event detection
The selection of the corresponding pin is performed through the RTC_TAFCR register as
follows:
● TAMP1INSEL is used to select which pin is used as the RTC_TAMP1 tamper input
● TSINSEL is used to select which pin is used as the RTC_TS time stamp input
● ALARMOUTTYPE is used to select whether the RTC_ALARM is output in push-pull or
open-drain mode
The output mechanism follows the priority order listed in Tabl e 3 0 and Tabl e 3 1.
Table 30. RTC_AF1 pin
(1)
Pin
configuration
and function
RTC_ALARM
enabled
RTC_CALIB
enabled
Tamper
enabled
Time
stamp
enabled
TAMP1INSEL
TAMPER1 pin
selection
TSINSEL
TIMESTAMP
pin
selection
ALARMOUTTYPE
RTC_ALARM
configuration
Alarm out
output OD
1 Don’t care Don’t care
Don’t
care
Don’t care Don’t care 0
Alarm out
output PP
1 Don’t care Don’t care
Don’t
care
Don’t care Don’t care 1
Calibration out
output PP
01Don’t care
Don’t
care
Don’t care Don’t care Don’t care
TAMPER1 input
floating
0 0 1 0 0 Don’t care Don’t care
TIMESTAMP
and TAMPER1
input floating
001100Don’t care
TIMESTAMP
input floating
0 0 0 1 Don’t care 0 Don’t care
Standard GPIO 0 0 0 0 Don’t care Don’t care Don’t care
1. OD: open drain; PP: push-pull.
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